Investigation of mutual influences of greenhouse effect and changes of dynamic and chemical processes in the UT/LS employing model simulations and observations
DLR-contribution to joint-project
Coupling of dynamics and atmospheric chemistry in the stratosphere: KODYACS
(Förderkennzeichen 07ATF43)
Martin Dameris, Christina Schnadt, Sigrun Matthes, Fabian Mager
DLR Institut für Physik der Atmosphäre, Oberpfaffenhofen, D - 82234 Wessling, Germany
The coupled chemistry-climate model E39/C has been employed for a couple of long-term simulations (decades), i.e. so-called time-slice experiments (with fixed boundary conditions) and transient simulations which cover the time period between the years 1960 and 2000. The model results have been compared with respective observations, which are mainly derived from ground based measurements and satellite instruments (e.g. Hein et al., 2001). Investigations of dynamical and chemical values and parameters, especially in the UT/LS region, have shown that the interactively coupled model system reproduce fairly well the climatological mean state of the atmosphere between the surface and the model top layer centred at 10 hPa. Moreover, observed variability and long-term changes (trends) which have been detected in recent decades are also satisfactorily simulated (e.g. Schnadt et al., 2002; Austin et al., 2003). The analyses of model data strongly indicate that the consideration of mutual effects of dynamical and chemical processes is necessary to realistically reproduce observed atmospheric features and behaviour. The importance of prescribed sea surface temperatures (SSTs) for the dynamic behaviour of the stratosphere in E39/C has been discussed by Schnadt and Dameris (2003), which clearly illustrates the coupling of the troposphere and the stratosphere. To improve the model system, a parameterisation scheme of photolysis frequencies at large solar zenith angles (SZA) has jointly been established with MPI-C (Mainz). It has been included in E39/C (Lamago et al., 2003). Considering large SZA (up to 93°) yield a more realistic description of dynamical and chemical processes, in particular in polar regions. An algorithm for a wave frequency analysis has been developed at DLR (Mager, PhD thesis, in preparation) to check the ability of E39/C to create the full spectrum of large-scale planetary waves in the troposphere and the stratosphere, which is necessary to generate the seasonal and inter-annual variability of the UT/LS, especially in the Northern Hemisphere. To get a better insight about the potentiality of currently available CCMs, and to estimate the importance of a well resolved UT/LS and the consideration of the entire stratosphere and mesosphere, a detailed comparison of the results of the transient simulations carried out with E39/C and MA-ECHAM/CHEM (MPI-C, Mainz; MPI-M, Hamburg) with long-term observations provided by DWD (Hohenpeißenberg) has been started. Additionally, a method has been evolved to determine tropopause height from gridded temperature data with coarse vertical resolution (Reichler et al., 2003), which helps to investigate changes in the UT/LS much better. A tropopause climatology derived from the CTM KASIMA (IMK, Karlsruhe) will now be used for E39/C validation purposes. Sensitivity simulations employing the Lagrangian CTM CLaMS (FZ Jülich), which are driven by meteorological fields provided by E39/C, have been used to check the importance of filamentary structures and small-scale mixing on the distribution of trace gases and to estimate the uncertainties in CCM with coarse horizontal resolution.
References:
Austin et al., Atmos. Chem. Phys., 3, 1-27, 2003.
Hein et al., Ann. Geophysicae, 19, 435-457, 2001.
Schnadt et al., Climate Dynamics, 18, 501-517, 2002.
Lamago et al., Atmos. Chem. Phys., 3, 1981-1990, 2003.
Reichler et al., Geophys. Res. Lett., 30(20), 2042, doi:10.1029/2003GL018240, 2003.
Schnadt and Dameris, Geophys. Res. Lett., 30, 1487, doi:10.1029/2003GL017006, 2003.